1. Field of the Invention
The present invention relates generally to a fuel vapor treating apparatus, in which the fuel vapor formed in a fuel tank is not to be released into the atmosphere but is to be collected and treated. More particularly, the present invention relates to a fuel vapor treating apparatus provided with a canister for collecting the fuel vapor and a device for suitably purging the fuel collected in the canister to an intake passage of an engine.
2. Description of the Related Art
There is a known fuel vapor treating apparatus to be mounted on a vehicle in which the fuel vapor evaporated in a fuel tank is not released into the atmosphere but is collected. Such apparatus is, for example, provided with a canister 183 in which the fuel vapor evaporated in a fuel tank 181 is collected through a vapor line 182, as shown in FIG. 14. The canister 183 contains an adsorbent 184 such as an activated carbon or the like. A purge line 185 extends from the canister 183 and is connected to an air intake passage 187 of an engine 186. In the canister 183, the fuel vapor introduced through the vapor line 182 is adsorbed in the adsorbent 184, and only the residual gas containing no fuel is exhausted through a vent 188 to the outside of the system. Further, during operation of the engine 186, the fuel collected in the canister 183 is, as necessary, purged through the purge line 185 to the air intake passage 187.
Japanese Unexamined Patent Publication No. Hei 4-347357 discloses another system. As shown in FIG. 15, in this apparatus, a vapor line 182 extending from a fuel tank is connected to a canister 190 via a first control valve 189 which is a ball check valve. This control valve 189 opens when the internal pressure of the tank exceeds a predetermined level due to evaporation of fuel in the tank. The opening of the first control valve 189 allows the fuel vapor contained in the tank to flow into the canister 190 through the vapor line 182.
A second control valve 193 and a third control valve 194 controlling an inlet 191 and an outlet 192, respectively, of the canister 190 are selectively opened depending on the balance between the internal pressure of the canister 190 and the atmospheric pressure. Both the control valve 193 and 194 are ball check valves. The second control valve 193 is let open so as to introduce outside air into the canister 190 when the fuel adsorbed in the canister 190 is to be purged to the air intake passage 187. Meanwhile, the third control valve 194 is let open to exhaust the gas containing no fuel from the canister 190 to the outside of the system whenever the internal pressure of the canister 190 exceeds a predetermined level.
Leakage of fuel vapor to the atmosphere, particularly that which leaks through the ports of tanks when fuel is charged to the tanks, wastes fuel. Thus, there are disclosed systems with respect to the above-described canister, which are designed to treat large amounts of fuel vapor formed during refueling. For example, U.S. Pat. No. 4,714,172 discloses such system which is provided, in addition to the vapor line, with a special breather line between the fuel tank and the canister. Fuel vapor, formed in large amounts in the tank during refueling, can be smoothly introduced to the canister through the breather line.
Only the fuel component of the fuel vapor introduced to the canister during refueling is collected in the canister, and the gas containing no fuel component is exhausted through a control valve disposed in an outlet opening to the atmosphere.
The amount of the fuel vapor flowing into the canister from the tank during refueling is great. Accordingly, if the control valve disposed in the breather line is a simple ball check valve, a great resistance is generated when the fuel vapor passes through the valve. This resistance inhibits smooth flow of the fuel vapor from the tank to the canister and increases the internal pressure of the tank. This increase of the internal pressure inhibits smooth refueling.
On the other hand, in order to treat such a large amount of fuel vapor with the adsorbent contained in the canister, the adsorbent must be constantly maintained to have sufficient fuel adsorbing capacity. Accordingly, when the fuel is to be purged from the canister, the fuel must be quickly released from the adsorbent by introducing a large amount of outside air into the canister. For this purpose, a ball check valve can conceivably be used as the control valve for controlling introduction of the outside air. However, if such is the case, it is difficult to introduce a large amount of outside air because the diameter of the ball check valve itself is small.
It is conceivable to employ a diaphragm check valve as the control valve in place of the ball check valve. The diaphragm check valve has a valve diameter larger than that of the ball check valve and allows a large amount of gas to pass through it. However, the diaphragm check valve, if employed as the control valve of the canister, causes some problems. One of the problems occurs when a purge control valve for controlling the purge amount is provided in the purge line, and the control valve is subjected to duty control. Here, in order to suitably control the purge amount from the canister, the actuation of the purge control valve can conceivably be subjected to electrical duty control. In this case, the pressure in the purge line is fluctuated by the opening and closing of the purge control valve, which are repeated intermittently. With this pressure fluctuation, the diaphragm check valve is allowed to repeat opening and closing motions. That is the diaphragm vibrates. Consequently, material fatigue is caused in the flexed portion of the diaphragm. In order to enhance resistance to such material fatigue, a diaphragm made of a special material or subjected to special treatment must be used. Further, the diaphragm is intermittently brought into contact with other members as it vibrates, and abrasion or damage to the other members occurs. Moreover, noise is generated by the vibration.
Another problem is that the entire size of the canister in which the diaphragm check valve is disposed is increased because the diaphragm check valve is larger than the ball check valve. The enlargement of the canister gives rise to a problem in mounting the canister within the limited space of a vehicle.
FIGS. 16 to 18 each show a canister 201 and control valves 204,205,206, which are diaphragm check valves. A partition 202 is disposed in the canister 201 to separate the interior into two chambers 203a,203b. The first control valve 204, which is connected directly to the first chamber 203a, is let open depending on the internal pressure of a fuel tank (not shown). The second control valve 205, which is connected directly to the second chamber 203b, is let open to introduce the air into the canister 201. The third control valve 206, which is also connected directly to the second chamber 203b, is let open to exhaust the gas containing no fuel from the canister 201.
FIG. 16 shows an up-down flow type canister 201 in which the fuel vapor flows in the vertical direction, when the canister 201 is mounted on a vehicle etc. In FIG. 16, control valve 206 disposed on the top of the canister 201 protrudes beyond the width L of the canister 201.
FIGS. 17 and 18 show a side flow type canister 201 in which the fuel vapor flows in the horizontal direction. Since the height H of this type of canister 201 can be reduced, this canister 201 is easier to mount on a vehicle. However, the control valves 205,206 protrude beyond the total height H of the canister 201.
Here, it is conceivable to connect the control valves 205,206 to the canister 201, for example, via hoses instead of connecting them directly to the canister 201. FIG. 19 shows a case where the control valves 205,206 are connected via hoses 207 to the canister 201. By locating the control valves 205,206 apart from the canister 201, the flexibility in mounting the canister 201 to a vehicle is increased.
However, in this construction, extra parts including the hoses 207, clamps 208, etc. for connecting the control valves 205,206 to the canister 201 are necessary. The added parts increase cost and assembly time. Further, fuel vapor may permeate through the hoses 207.